This invention relates to a die which is split into three sections in the axial direction of the die and used to vulcanize a tire or other elastomeric articles.
A conventional split vulcanizing die is described in the Japanese Patent Application (OPI) No. 78711/85 (the term "OPI" is used herein means an "unexamined published application"). In this conventional die, the inside circumferential surface of an outer ring for moving a number of segments is shaped as a truncated cone, and the outside circumferential surface of each of the segments is shaped as a truncated cone having the same taper as the former. When the outer ring is pushed in to move the segments inwards in the radial direction of the die into contact with an upper and a lower molding ring, the truncated-cone-shaped circumferential surfaces of the outer ring and each of the segments are brought into complete surface contact with each other.
When the outer ring is pulled away from the segments in the axial direction of the die, to move the segments outwards in the radial direction of the die, a gap is created between the truncated-cone-shaped circumferential surface of the outer ring and both the circumferential ends of each of the the segments. This occurs because the radius of curvature of each of the truncated-cone-shaped circumferential surfaces of the outer ring and the segments varies in the axial direction of the die. Hence, the outer ring and each of the segments come into line contact with each other. Because of this line contact, the outer ring and the segments undergo local wear and the posture of each of the segments deteriorates, so that smooth operation cannot be attained.
In order to solve such a problem, another known split vulcanizing die described in the Japanese Patent Application No. 28295/71 has been proposed. In this die, a plurality of cam blocks are fitted to the inside circumferential surface of an outer cylindrical ring. The inside of the cam blocks is provided with oblique planar surfaces of the same gradient as each other. The circumferential outsides of segments are provided with oblique planar surfaces of the same gradient as those of the cam blocks, and the oblique planar surfaces of the cam blocks and the segments are located in slip contact with each other. However, when the segments are pushed onto upper and lower molding rings, a high shearing force acts between the outer ring and each of the cam blocks. If the cam blocks are joined to the outer ring by bolts, a deviation is caused between the outer ring and each cam block. This tends to deteriorate the dimensional accuracy of the die or in extreme cases, the bolts are broken. In order to solve such a problem, the cam blocks could be firmly joined to the outer ring by welding, but the inside surfaces of the cam blocks would require difficult cutting after the welding. For that reason, this die has not been put into practical use.
In order to solve the above-mentioned problems, still another conventional split vulcanizing die has been proposed. In this die, illustrated in FIG. 1, the circumferential inside of an outer ring 61 is provided with a plurality of recesses 62 at equiangular intervals in the circumferential direction of the die. The bottom of each of the recesses 62 in an oblique planar surface 63 and segments 64 are inserted into the recesses 62. The circumferential outsides of the segments 64 are provided with flat surfaces 65 which are placed in slip contact with the oblique flat surfaces 63. However, since the recesses 62 are provided in the inside circumferential surface of the outer ring 61, the cost of processing of the die to achieve the required accuracy is high.